Method of treating cracked petro



Dec. 28, 1937. R. c. OSTERSTROM METHOD 0F TREATING CRACKED PETROLEUMDISTILLATES Original Filed Feb. 54, `1930 Rioni-11j l of unsaturationthan the simple oleflnes.

Reissued Dec. 28, 1937 UNITED STATES PATENT OFFICE METHOD OF TREATINGCRAOKD PETRO- LEUM DISTILLATES Rudolph C. Osterstrom, Kenilworth, andCary R. Wagner, Chicago, Ill., assignors to The Pure Oil Company,Chicago, IIL, a corporation of Ohio 8 Claims.

This invention relates to improvements in processes for treating crackedpetroleum oils and similar products resulting from the cracking ofheavier oils in the vapor phase for the production of such lighter oilsand products therefrom.

Cracked distillates obtained by the vapor phase cracking of hydrocarbonoils contain high percentages of unsaturated constituents and especiallyunsaturated constituents of a higher. degree Such highly crackeddistillates contain undesirable gum-forming and color-impartingcompounds consisting of the highly reactive unsaturates which readilyoxidize upon exposure to air, o-r when stored in tanks, to produce gummyor resinous bodies in such quantities as to render the crackeddistillates unsuitable when not adequately treated for use as motorfuels or blending stocks. Hithertoit has been common in the art toeffect the removal of the undesirable gumforming and color-impartingbodies from cracked distillates obtained by the vapor phase conversionof heavier hydrocarbon oils, by bringing the vapors of such cracked oilsinto contact with 2-51 fulle-rs earth which apparently acts as acatalyst in effecting the polymerization of the aforesaid undesirablecompounds. Again the distillates have been treated with sulphuric acidand subsequently neutralized by an alkalito rid the distillates ofobjectionable color and gums.

Itis a primary object of the present invention to provide an improvedprocess for effecting the removal of these undesirable compounds whichare present in the cracked distillates in a more economical andeffective manner and to provide a system of treatment wherein the use ofrelatively expensive treating materials is reduced to a minimum andwherein only the heavier fractions of the distillates undergoingtreatment require the use of a polymerizing agent, the lighterfractionsbeing thoroughly and effectively treated to remove theundesirable compounds without requiring the use of any extraneoustreating agent whatever.

`For a, more complete understanding o-f the present invention referenceis to be had to the accompanying drawing wherein the figure illustratesdiagrammatically apparatus used in carrying out the present invention.

Referring more particularly to this drawing', the

numeral I designates a pipe still in the setting of which there isarranged a bank of heating tubes 2. The cracked distillate delivered tothe system for treatment is continuously passed through the tubes 2 andis heated to vaporizing temperatures while passing through said tubes ofthe order of 500 to 650 F. This distillate is obtained from a storagetank 3 and is withdrawn from the tank and forced through the coils ofthe tubes 2 by means of a pump 4 which places the oil passing throughthe pipe still under pressures of the order of from 300 to 500 poundsper square inch. 'I'hese pressures, however, are not suicient tomaintain the oils in the liquid phase at the temperatures to which theoils are heated prior to their discharge from the coils comprising thebank 2. Care is taken, however. in the operation of the still I to avoidheating the oils to cracking temperatures since the object of this phaseof the treatment is to vaporize the oils while the latter are maintainedunder superatmospheric pressures Without any substantial cracking of theoils. It will be understood that the oils o-r distillates contained inthe tank 3 are obtained preferably from the operation of vapor phasesystems of oil conversion wherein heavier oils are heated to vaporizingand cracking temperatures in excess of 1000 F. The subsequentlycondensed and fractionated distillates are then delivered to the tank 3to remove therefrom undesirable color and gum producing compounds, andit is to the performance of this function that the present invention isdirected.

A vapor discharge line'5 extends from the outlet side of the coil 2 tothe lower portion of a fractionating tower 6. This tower may be of anystandard construction and of suflicient mechanical strength to withstandthe super-atmospheric pressures which are set uptherein by the operationof the system. In this instance the tower has been shown as consistingof a plurality of horizontally arranged vertically spaced trays 1through which the light vaporous products pass in a generally upwarddirection, the undesirable heavy compounds which condense under theternperature and pressure conditions existing in the tower are collectedas liquids in the lower portion of the tower. In this instance, theupper portion of the tower is provided with a pressure relief valve 8-to permit of the release of abnormal pressures which may accidentallyexist in the tower.

We have discovered that when cracked petroleum distillates having theboiling range of ordinary gasoline are thus vaporized to elevated butnon-cracking temperatures and maintained at the same time undersuper-atmospheric pressure conditions for relatively prolonged periodsof time, the undesirable fraction of the unsaturated compounds areapparently polymerized in the treating zone indicated by the tower 6.'The polymerization is evident in the production of higher boiling pointoils than they boiling points of the oils initially introduced into thesystem by the pump 4. These high boiling point oils, obtained bypolymerization in the tower 6, are removed from the bottom of the towerby way of the valved pipe line 9 in the form of a fuel oil residue. Theperiod of time, which is an important factor, taken by the distillatesunder treatment in securing this polymerization varies, of course, withthe character of the charging stock and operating conditions, since thedistillates may be maintained in the system for periods of time varyingbetween 15 minutes to three hours, but preferably not in excess ofminutes.

'I'he lighter oils which remain in a vaporous state following travelthrough the tower 6 are withdrawn by way of an overhead line IIJ andpass to a condenser II wherein the vapors are reduced to a liquid statewhile still maintained un-der super-atmospheric pressures. Thesecondensed oils then flow by way of a pipe line I2 -to a gas separatorI3. The pipe line I2 contains al pressure relief valve I4 so that theproducts delivered into the separator I3 will be under ordinary oratmospheric pressures. Such fixed gas as may be formed as a result ofthe operation is withdrawn from the top of the separator I3 by way ofthe pipe line I5.while the treated distillate is removed from theseparat-or by way of a pipe line I6 and lead to a storage tank I1 asfinished motor fuel.

In a typical run, in accordance with the features of the presentinvention, a distillate obtained by the vapor phase cracking of heavyhydrocarbon oils was delivered under a pressure of 375/pounds to thepipe still and which distillate possessed an A. P. I. gravity of 52, aninitial boiling point of 95 F., an end point of 440 F., and was of adecided lemon yellow color. This stock was heated in the still to atemperature of 550 F. and fractionated in the tower Ii and thisdistillate when Ydelivered to the tank I'I was found upon analysis topossess an initial boiling point of 95 F., an end boiling point of 385F.,

an A. P. I. gravity of 56, and a clear water white color (Saybolt plus25). Approximately 60% of the original charging distillate thus treatedwas recovered` as a finished motor fuel product in the tank I1. Inaddition to its water white color the motor oils collected in the tankI'I possess a low or negligible gum content which remains substantiallyuniform under ordinary conditions of storage and handling.

The polymerized fractions which are removed from the bottom of thefractionating tower by way of the pipe line 9 were found to possess,upon analysis, an A. P. I. gravity of 20, an initial boiling point of420 F., and an end boiling point of 700 F. The relative differences inthe matter of gravity and boiling range in the cracked distillateinitially introduced into the pipe still I and the residue removed fromthe bottom of the tower 6 indicate strongly the polymerizationconditions which are set up in the tower 6 by subjecting the vapors ofthe cracked distillate to the elevated temperatures and pressures forvarying periods of time.

The lower trays of the fractionating tower 6 are provided with a liquidoutlet line I8 by which oils heavier than those delivered to the tank IIbut lighter than the fuel oils removed by way of the pipe line 9, aredischarged from the tower 6. The oils leaving the line I8 may be termeda heavy gasoline since a typical cut thereof discloses that they possessan initial boiling point of approximately 300 F., an end boiling pointof 430 F., an A. P. I. gravity of 43.0 and a Saybolt color varying fromminus 10 to plus 5, and comprise from 20 to 35% of the total volume ofoil delivered to the pipe still I. To render these heavier motor fueloils suitable for commercial purposes, it is advisable that they shouldbe treated with sulphuric acid and a neutralizing alkali which may bedone by extending the line I8 to a mixer I9 wherein the oils are broughtinto contact with suitably regulated quantities of sulphuric acid. Uponleaving the mixer the oils are neutralized with caustic introduced as at20 into the outlet line 2| of the mixer I9. These oils are then passedthrough a heater 22 in which they are redistilled and are nallydischarged into a separating tower 23. 'Ihe polymerized oils arewithdrawn from the bottom of the tower 23 and delivered to a tank 24,whereas the light vaporous oils pass overhead from the tower 23, arecondensed as at 25 and delivered as a nished motor fuel to the tank 26.

By this method of treatment a large part of the cracked distillate doesnot require treatment with any added polymerizing agent, since theconditions of temperature, pressure and time brought to bear on thevapors passing through the tower 6 are suiiicient of themselves tosecure the desired polymerization without necessitating the aid ofextraneous treating agents. This results in a very considerable economyin operation since the expense of treating agents such as fullers earthand sulphuric acid is reduced to a minimum, sulphuric acid treatmentbeing only employed in connection with the heavier oils removed from thebottom of the tower by way of the outlet line I8. Moreover, the systemavoids the loss of the oil or distillate itself which inevitably occurswhen large quantities of treating agents are employed, and in thisrespect the total percent of usable distillates recovered from thesystem is higher than from comparable systems of which we haveknowledge. Again, the system operates to avoid injury to the oilsundergoing treatment. For example, if the lighter oils obtained from thesysteml by way of the tank I1 were to be treated with concentratedsulphuric acid, a large percent of the desirable compounds present inthese oils as well as the undesirable constituents, would be attacked bythe acid and lost as a residue or sludge. Therefore, in accordance withthe present invention these lighter oils are not in any way brought intocontact with an active polymerizing agent so that there can be anyinjury to these light oils or loss in their total volume as a result oftreatment. The heavy motor fuel oils removed from the fractionatingtower 6 by the outlet line I8 are capable of withstanding treatment withsulphuric acid without injurious results or burning of the oil so thatthere is a large recovery of this relatively heavier fraction of thedistillates as a.

treated, gum-free motor fuel of desired color. The polymer-containingfraction removed from the bottom of the tower 6 by way of the pipe line9 is used preferably as a fuel oil and is not subjected to furthertreatment.

The present invention thus provides for the vaporizing of the crackeddistillates and the fractionation thereof at high pressures by which thenecessary time factor in obtaining polymerization reactions is securedin a tower of ordinary size. 'Ihe use of pressure is also advantageousin promoting the desired polymerization reactions, because one moleculeof a polymerized product occupies no more space than a single moleculeof the compounds entering into the polymerizing reaction, the reactionsbeing speeded up, as it were, by the use of higher pressures.

When an ordinary cracked Vapor phase distillate is fractionated at lowpressures and in the usual manner, and where the vapors have a velocityof approximately one foot per second through a fraction tower of theusual type, the resulting product is yellow in color from the beginningof the distillation to the end. We have discovered that when thefractionation is slowed down so that the vapors are subjected totemperatures above 200|o F. for a period of minutes in an ordinaryfractionating tower, colorless products distill over, and from thisbasis we have continued to increase the elements of time, pressure andtemperature to secure the most practical conditions for commercialoperation. In ordinary operations less than 2% of the cracked distillateunder treatment is lost as a result of polymerization reactions, andfully 50% of the distillate so treated may be recovered in the form of agum-free and colorless liquid which requires no treatment withcatalyzing agents. Ordinarily, between 50 and 75% of the distillateunder treatment may be so recovered after treatment without a catalyzingagent, thus leaving only the high boiling fractions with a distillationrange of between 300 F. and 430 F. which require polymerizationtreatment with, for example, sulphuric acid. Of this latter fraction,approximately 95% thereof is obtained as a salable motor fuel product ofdesired color and freedom from gums.

What is claimed is:

l. The method of treating cracked low boiling petroleum oils containingunsaturated compounds to remove therefrom gum-forming andcolor-imparting bodies, which comprises heating such oils totemperatures above their normal vaporizing temperatures but insuiiicientto effect any substantial cracking thereof, introducing such heated oilsalone and unmixed with other substances into a fractionating zonewherein said oils in a vapor state are maintained under superatmosphericpressures, retaining the oils in said zone while in substantially thevapor state and under the influence of said pressures for a sufficientperiod of time not in excess` of thirty minutes to effect the formationof compounds having a higher boiling range than that of the oilsoriginally heated, withdrawing from one portion of said fractionatingzone the treated vaporized oils, and separately withdrawing from anotherportion of said fractionating zone as liquids the oils containing thehigh boiling compound.

2. The method of treating cracked low boiling petroleum oils containingunsaturated compounds to remove therefrom gum-forming andcolor-imparting bodies, which comprises subjecting such oils alone whileunder super-atmoscompounds as liquid oils from said fractionating zone,separately removing the vaporized oils from another portion of saidfractionating zone and condensing the same without release of pressure,releasing the pressure on said condensed oils and removing lightergaseous products therefrom.

`3. The method of treating cracked low boiling petroleum oils containingunsaturated compounds to remove therefrom gum-forming andcolor-imparting bodies, which comprises subjecting such oils alone andunmixed with other substances to temperatures sufficiently high toeffect their complete vaporization without any material cracking of thesame, introducing such vaporized oils alone into a fractionating zonewherein the oils are maintained under super-atmospheric pressures,retaining the oils in such zone while in substantially the vapor stateand under the influence of said pressures for a suicient period of timenot in excess of thirty minutes to effect polymerization of theundesired unsaturated compounds contained therein, removing from onepoint of said fractionating zone the undesired compounds in the form ofa heavy liquid oil, and in removing from another point of saidfractionating zone the desired treated vapors, and condensing andcollecting said vapors.

4. The method of treating cracked low boiling petroleum oils containingunsaturated compounds to remove therefrom gum-forming andcolor-imparting bodies, which comprises subjecting such oils alone andunmixed with other substances to temperatures sufliciently high toeffect substantially their complete vaporization without any materialcracking of the same, introducing such vaporized oils alone into a.fractionating zone wherein the oils are maintained undersuper-atmospheric pressures and held in said zone for a sufficientperiod of time Varying between fifteen minutes and three hours insubstantially the vapor state to effect the polymerization of theundesired compounds contained therein, withdrawing the treated vaporsfrom the upper portion of said fractionating zone and condensing andcollecting the same, separately withdrawing from the lower portion ofsaid fractionating zone a heavy liquid oil containing the undesiredpolymerized compounds, and withdrawing from an intermediate portion ofsaid zone an intermediate fraction of said liquid oil and subjectingsaid intermediate fraction to treatment with polymerizing reagents.

5. The method of removing gum-forming and color-imparting bodies fromlow boiling cracked oil vapors which consists in contacting said vaporsin a fractionating zone with a plurality of bodies of liquidhydrocarbons at temperatures above the vaporizing temperature ofgasoline but below cracking temperature and at high superatmosphericpressure for a period of time ranging from approximately l5 minutes to 3hours, and condensing the degummed vapors.

6. Method in accordance with claim 5 in 8. Method in accordance withclaim 5 in which the liquid hydrocarbons are condensed which the vaporsare contacted with the liquid fractions of the vapors. bodies attemperatures of 500-650. F. and at 7. Method in accordance with claim 5in pressures of 30D-500 pounds per square inch.

5 which the vapors are contacted with the liquid RUDOLPH C. OSTERSTROM.

bodies at temperatures of 5U0650 F. CARY R. WAGNER.

